U.S. patent number 7,647,206 [Application Number 11/532,453] was granted by the patent office on 2010-01-12 for system and method for monitoring structures for damage using nondestructive inspection techniques.
This patent grant is currently assigned to The Boeing Company. Invention is credited to Robert G. Ford.
United States Patent |
7,647,206 |
Ford |
January 12, 2010 |
System and method for monitoring structures for damage using
nondestructive inspection techniques
Abstract
A system and method for monitoring a structure for damage is
provided. The method includes stimulating a sensor in a sensor
array to generate a plurality of waves. The sensor array includes
one or more quadrants, wherein each quadrant includes one or more
sensors. Sensor data from all sensors are acquired in each quadrant
in parallel. The sensor data wave characteristics is processed for
analysis. The processed sensor data wave characteristics are
compared with threshold values to determine the presence of damage
to the structure. If the presence of damage is determined, a
corrective system is notified for corrective action.
Inventors: |
Ford; Robert G. (Snohomish,
WA) |
Assignee: |
The Boeing Company (Chicago,
IL)
|
Family
ID: |
40900072 |
Appl.
No.: |
11/532,453 |
Filed: |
September 15, 2006 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
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US 20090192727 A1 |
Jul 30, 2009 |
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Current U.S.
Class: |
702/183; 73/583;
702/35; 702/34 |
Current CPC
Class: |
G01N
29/4409 (20130101); G01N 2291/2694 (20130101); G01N
2291/106 (20130101) |
Current International
Class: |
G01N
29/00 (20060101); G06F 17/40 (20060101) |
Field of
Search: |
;702/183,34-36 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Bulut et al.; "Real-time Nondestructive Structural Health
Monitoring using Support Vector Machines and Wavelets"; Aug. 2004;
Seattle, USA. cited by other .
Sun et al.; "Statistical-based Structural Health Monitoring Using
Wavelet Packet Transform". (No date provided). cited by
other.
|
Primary Examiner: Wachsman; Hal D
Claims
What is claimed is:
1. A method for monitoring a structure for damage, comprising:
stimulating a sensor in a sensor array to generate a plurality of
waves, wherein the sensor array includes one or more quadrants,
wherein each quadrant includes one or more sensors; acquiring
sensor data from all sensors in each quadrant in parallel, the
sensor data including one or more wave characteristics; processing
the sensor data wave characteristics for analysis; comparing the
processed sensor data wave characteristics with threshold values to
determine the presence of damage to the structure; and notifying a
corrective system if the presence of damage is determined, for
corrective action.
2. The method of claim 1, wherein the sensor data is a series of
data samples representing a wave captured over a period of
time.
3. The method of claim 1, wherein the wave is propagated over the
surface of the structure.
4. The method of claim 1, wherein interrogation time is independent
of the number of sensor arrays.
5. The method of claim 1, wherein each sensor in the sensor array
is stimulated.
6. The method of claim 1, wherein each sensor is a transducer.
7. The method of claim 1, further comprising multiplexing the
sensor data from each quadrant into a single channel.
8. The method of claim 7, wherein the sensor data for each path
from each quadrant is acquired simultaneously.
9. The method of claim 8, further comprising transmitting sensor
data using a plurality of single channels from each quadrant to a
computational engine where the data is compared with threshold
values stored in a processing module.
10. The method of claim 9, wherein the structure has a plurality of
sensor arrays; wherein each sensor in each of the sensor arrays is
stimulated; and wherein the sensor data from all sensors in the
sensor arrays are collected and used to determine the presence of
damage on the structure.
11. The method of claim 9, wherein damage occurs when the sensor
data is equal to or greater than the threshold values.
12. The method of claim 11, wherein the structure is between at
least two adjacent transducer arrays; and wherein the at least two
adjacent transducer arrays are stimulated simultaneously.
13. A method for monitoring a structure for damage, comprising: (a)
laying out a plurality of sensor arrays on the structure; wherein
each of the plurality of sensor arrays includes a plurality of
quadrants; wherein each quadrant in the plurality of quadrants
includes a plurality of sensors; (b) continuously acquiring sensor
data from all sensors in each quadrant in parallel, wherein sensor
data including one or more wave characteristics; (c) processing the
sensor data wave characteristics for analysis; (d) comparing the
processed sensor data wave characteristics with threshold values to
detect damage to the structure; (e) repeating steps (b)-(d) so as
to detect damage to the structure; and (f) notifying a corrective
system if the damage to the structure is detected, for corrective
action.
14. The method of claim 13, wherein each sensor is a
transducer.
15. The method of claim 13, further comprising multiplexing the
sensor data from each of the quadrant into a plurality of single
channels with a single channel for each quadrant.
16. The method of claim 15, wherein the sensor data from each
quadrant is acquired simultaneously.
17. The method of claim 16, further comprising transmitting the
sensor data using the plurality of single channels from each
quadrant to a computational engine where the sensor data is
compared with threshold values stored in a processing module.
18. The method of claim 17, wherein damage occurs when the sensor
data is equal to or greater than the threshold values.
19. A system for monitoring a structure for damage, comprising: a
plurality of sensor arrays on the surface of the structure; wherein
each sensor array in the plurality of sensor arrays includes a
plurality of quadrants; and wherein each quadrant in the plurality
of quadrants includes a plurality of sensors; and a plurality of
network detection modules; wherein each network detection module in
the plurality of network detection modules acquires sensor data
from all sensors in each quadrant in parallel, the sensor data
including one or more wave characteristics; wherein each network
detection module includes a plurality of multiplexers for
multiplexing the sensor data from each quadrant for transmission
into a plurality of single channels with a single channel for each
quadrant and a computational engine for comparing the wave
characteristics from the plurality of single channels with
predetermined thresholds to determine the presence of damage to the
structure.
20. The system of claim 19, wherein the sensor data is a series of
data samples representing a wave captured over a period of
time.
21. The system of claim 20, wherein the wave is propagated over the
surface of the structure.
22. The system of claim 19, wherein interrogation time is
independent of the number of sensor arrays.
23. The system of claim 19, wherein each sensor in the sensor array
is stimulated.
24. The system of claim 19, wherein each sensor is a
transducer.
25. The system of claim 19, wherein each multiplexer multiplexes
the sensor data from one of the quadrant into a single channel.
26. The system of claim 25, wherein a path data from each quadrant
is acquired simultaneously.
27. The system of claim 26, wherein the sensor data is transmitted
using single channel each quadrant to a computational engine where
the sensor data is compared with threshold values stored in a
processing module.
28. The system of claim 27, wherein damage occurs when the sensor
data is equal to or greater than the threshold values.
29. A system for monitoring a structure for damage, comprising: a
plurality of sensor arrays disposed about the boundaries of the
structure and between the boundaries of the structure; wherein each
sensor array in the plurality of sensor arrays includes a plurality
of quadrants; and wherein each quadrant in the plurality of
quadrant includes a plurality of sensors; and a plurality of
network detection modules; wherein each network detection module in
the plurality of network detection modules acquires sensor data
from all sensors in each quadrant in parallel, the sensor data
including one or more wave characteristics; where each of the
network detection modules are synchronized causing sensors on a
first sensor array on a first boundary of the structure to acquire
stimulus originating from a second sensor array on a second
boundary of the structure; wherein each network detection module
includes a plurality of multiplexers for multiplexing the sensor
data from each quadrant into a plurality of single channels with a
single channel for each quadrant and a computational engine for
comparing the wave characteristics from the plurality of single
channels with predetermined thresholds to determine the presence of
damage to the structure.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
None
BACKGROUND
1. Field of Invention
The present invention relates generally to inspecting structures
for damage, and more particularly to detecting structure damage by
using a sensor array laid on the structure.
2. Background of the Invention
Certain structure failures may result in loss of property and life.
For example, aircraft structure failures may be catastrophic.
Hence, it's prudent to monitor such structures to avoid
catastrophic failures.
Non-Destructive Inspection (NDI) techniques are used to monitor
such structures. One such technique is based on propagating a wave
through an aircraft structure and then observing the echo. This is
achieved by placing a probe, containing an ultrasonic transducer,
on the structure. The wave propagates through the aircraft in a
Z-axis (i.e. the axis which is normal to the surface of the
structure). This technique can only inspect a very small area of
the aircraft. To monitor and detect damage on a large aircraft
structure (for example the wing structure) will require a large
number of sensors. This will also increase use of hardware and add
weight to the inspection system.
In view of the above, what is needed is a method and system for
efficiently monitoring a large area of a structure using one or
more stimuli on a large number of sensors.
SUMMARY OF THE INVENTION
In one aspect of the present invention, a method for monitoring a
structure for damage is provided. The method includes stimulating a
sensor in a sensor array; wherein the sensor array includes one or
more quadrants; wherein each quadrant includes one or more sensors;
acquiring sensor data from all sensors in each quadrant in
parallel; processing the sensor data for analysis; comparing the
processed sensor data with threshold values to determine the
presence of damage to the structure; and notifying a corrective
system of the damage for corrective action.
In another aspect of the present invention, a method for monitoring
a structure for damage is provided. The method includes (a) laying
out a plurality of sensor arrays on the structure; wherein each of
the plurality of sensor arrays includes a plurality of quadrants;
wherein each quadrant in the plurality of quadrants includes a
plurality of sensors; (b) continuously acquiring sensor data from
all sensors in each quadrant in parallel; (c) processing the sensor
data for analysis; (d) comparing the processed sensor data with
threshold values; (e) repeating steps (b)-(d) until damage to the
structure is detected; and (f) notifying a corrective system of the
damage for corrective action.
In yet another aspect of the present invention, a system for
monitoring a structure for damage is provided. The system includes
a plurality of sensor arrays on the surface of the structure;
wherein each sensor array in the plurality of sensor arrays
includes a plurality of quadrants; and wherein each quadrant in the
plurality of quadrants includes a plurality of sensors; and a
plurality of network detection modules; wherein each network
detection module in the plurality of network detection modules
acquires sensor data from all sensors in each quadrant in parallel;
wherein each network detection module includes a plurality of
multiplexers for multiplexing the sensor data from each quadrant
into a plurality of single channels with a single channel for each
quadrant and a computational engine for comparing the plurality of
single channels with predetermined thresholds to determine the
presence of damage to the structure.
In yet another aspect of the present invention, system for
monitoring a structure for damage is provided. The system includes
a plurality of sensor arrays on the boundaries and between the
structure; wherein each sensor array in the plurality of sensor
arrays includes a plurality of quadrants; and wherein each quadrant
in the plurality of quadrants includes a plurality of sensors; and
a plurality of network detection modules; wherein each network
detection module in the plurality of network detection modules
acquires sensor data from all sensors in each quadrant in parallel;
where each of the network detection modules are synchronized
causing sensors on a first sensor array on a first boundary of the
structure to acquire stimulus originating from a second sensor
array on a second boundary of the structure; wherein each network
detection module includes a plurality of multiplexers for
multiplexing the sensor data from each quadrant into a plurality of
single channels with a single channel for each quadrant and a
computational engine for comparing the plurality of single channels
with predetermined thresholds to determine the presence of damage
to the structure.
This brief summary has been provided so that the nature of the
invention may be understood quickly. A more complete understanding
of the invention can be obtained by reference to the following
detailed description of the preferred embodiments thereof in
connection with the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing features and other features of the present invention
will now be described with reference to the drawings of a preferred
embodiment. The illustrated embodiment is intended to illustrate,
but not to limit the invention. The drawings include the
following:
FIG. 1 illustrates a block diagram of a system for monitoring a
large area of a structure for damage according to one aspect of the
present invention;
FIG. 2 is functional block diagram of the system and method for
monitoring a structure for damage of FIG. 1;
FIG. 3 is a top-level block diagram of a processing module
according to one aspect of the present invention;
FIG. 4 illustrates the internal architecture of a network detection
module, according to one aspect of the present invention;
FIG. 5 illustrates an example of a transducer grid, according to
one aspect of the present invention;
FIG. 6 illustrates an example of a quadrant in a transducer grid,
according to one aspect of the present invention;
FIG. 7 illustrates an electronically stimulated sensor causing a
structure to produce and propagate a surface wave to a second
sensor;
FIG. 8 illustrates an example of usable path data from a single
stimulated sensor;
FIG. 9 is a flow chart for actively detecting structure damage,
according to one aspect of the present invention;
FIG. 10 is a flow chart for passively structure damage, according
to one aspect of the present invention;
FIG. 11 illustrates an example of acquiring structural path data
from a single sensor as illustrated in FIG. 8;
FIG. 12 illustrates an example of interrogating the structure
between two or more adjacent transducer arrays, according to one
aspect of the present invention; and
FIG. 13 illustrates an example of pulse--echo acquisition,
according to one aspect of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following detailed description is of the best currently
contemplated modes of carrying out the invention. The description
is not to be taken in a limiting sense, but is made merely for the
purpose of illustrating the general principles of the invention,
since the scope of the invention is best defined by the appended
claims.
According to the present invention, a Structural Health Monitoring
(SHM) System and method for monitoring a large area of a structure
for damage using one or more stimuli for a sensor array is
provided. Although the method of the present invention is
implemented using an aircraft, those skilled in the art will
recognize that the principles and teachings described herein may be
applied to a variety of structures, including, but not limited to,
buildings, automobiles, ships, helicopters, and trains.
The practicality and acceptance of the SHM System is dependent on
achieving fast damage detection using Non-Destructive Inspection
(NDI) techniques while minimizing the cost, weight and size of the
system. The SHM system of the present invention places multiple
sensor arrays on a structure and utilizes both active and passive
structural damage detection. In active structural damage detection
systems, a single sensor in a sensor array stimulates the structure
under test while the other sensors in the sensor array measure the
resultant structural response. This process continues until all
sensors in all of the sensor arrays have been stimulated. In
passive structural damage detection, sensors do not stimulate the
structure; they simply monitor the structure to detect stress or
loads beyond pre-determined limits.
Turning to FIG. 1, a block diagram of a SHM system 5 for monitoring
a large area of a structure 2 for damage using a single stimulus on
a large number of sensors, according to one aspect of the present
invention is illustrated. In system 5, a plurality of sensor arrays
4, 6, 8, 10 are laid on the surface of structure 2 and connected to
a plurality of network detection modules (NDMs) 12, 14, 16, 18
respectively. Each NDM 12, 14, 16, 18 provides a stimulus to a
sensor in corresponding sensor arrays 4, 6, 8, 10 as well as the
electrical interface necessary to capture or acquire the sensor
data from sensor arrays 4, 6, 8, 10, i.e. the resultant structural
response captured by all the other sensors in sensor arrays 4, 6,
8, 10. Although four NDMs and four sensor arrays are illustrated in
FIG. 1, a greater or lesser number of NDMs and arrays may be
utilized.
Damage is detected by comparing processed sensor data to threshold
values stored in a processing module 20. Threshold values are based
on allowable damage type and size for the type of structure from
previous testing or from the prior occurrences of damage to the
same type of structure. Processing module 20 instructs each NDM 12,
14, 16, 18 to send a stimulus to respective sensor arrays 4, 6, 8,
10, collect the sensor data and send the collected data to the
processing module 20 then processing module 20 determines the
presence of any damage on structure 2 by comparing the processed
sensor data with the threshold values. Sensor data is transmitted
from NDMs to processing module 20 using any known type of
transmission 19, such as, wireless, Ethernet, and Fibre
Channel.
Damage has occurred when the processed sensor data is equal to or
greater than the threshold values. If damage is detected,
processing module 20 notifies a corrective system 22, such as the
airplane maintenance system, that there is a problem that requires
correction.
A large area of structure 2 is inspected for damage using one or
more stimuli on a large number of sensors. Instead of propagating
the wave through structure 2 in the Z-axis as in the prior art, the
present invention propagates the wave along the surface of
structure 2 (i.e. Bulk, Rayleigh or Lamb waves in the x and y
axis). The collected sensor data includes wave characteristics as
the waves travel along the surface, i.e. reflections of the
traveling waves, diffractions of the waves or a dispersion curve of
the waves which indicates the nature or quality of the material or
structure being inspected or monitored.
FIG. 2 is a functional block diagram of the steps and processes of
FIG. 1 used to capture, analyze and transmit the sensor data to
corrective system 22. A NDM functional block 24 comprises a
stimulate function 26 and an acquire function 28 for stimulating
sensors and acquiring sensor data from surrounding sensors in the
sensor arrays. A control and process function 30 instructs
stimulate function 26 to stimulate a sensor in sensor arrays 4, 6,
8, 10 and instructs acquire function 28 to acquire or collect data
from all sensors in sensor arrays 4, 6, 8, 10. The collected sensor
data is processed in control and process function 30 to determine
the presence of any damage on structure 2 and notify corrective
system 22 of any damage.
FIG. 3 is a block diagram of processing module 20, according to one
aspect of the present invention. Processing module 20 includes a
computer-readable memory storage device 34 for storing readable
data. Storage device 34 may include a hard drive, a magnetic tape,
a magnetic drum, integrated circuits, or the like, operative to
hold data by any means, including magnetically, electrically,
optically and the like. Storage device 34 stores operating system
program files, application program files, computer-executable
process steps of the present invention, web-browsers and other
files. Some of these files are stored on storage device 34 using an
installation program. For example, a microprocessor 36 executes
computer-executable process steps of an installation program so
that microprocessor 36 can properly execute the application
program. Processing module 20 may also access computer-readable
data files, application program files, and computer executable
process steps embodying the present invention or the like via a
removable memory device 38 (for example, a CD-ROM, a CD-R/W, a
flash memory device, a Zip drive, a floppy disk drive, etc.).
Microprocessor 36, storage device 34, and removable memory device
38 typically interface with a computer bus 40.
A CANBUS, AFDX, ARINC 429, ARJNC 629, modem, integrated services
digital network (ISDN) connection, or the like (not shown) also
provides processing module 20 with a network connection.
Also shown in FIG. 3 is an NDM interface 41, interfacing with
computer bus 40 that operatively connects NDMs 12, 14, 16, 18 (as
shown in FIG. 1) to processing module 20.
A random access memory ("RAM") 42 also interfaces with computer bus
40 to provide microprocessor 36 with access to random access
memory. When executing stored computer-executable process steps
from storage device 34, microprocessor 36 stores and executes the
process steps out of RAM 42.
A read only memory ("ROM") 44 is provided to store invariant
instruction sequences such as start-up instruction sequences or
basic input/output operating system (BIOS) sequences. ROM 44 also
interfaces with computer bus 40.
Processing module 20 can be connected to other computing systems
and corrective system 22 through a network interface 46 using
computer bus 40 and a network connection (not shown). Network
interface 46 may be adapted to one or more of a wide variety of
networks, including local area networks, storage area networks,
wide area networks, the Internet, and the like.
In one aspect of the invention monitoring software may be supplied
on a CD-ROM or a floppy disc, or alternatively it could be read
from the network via network interface 46. In yet another aspect of
the invention, processing module 20 can load the monitoring
software from other computer readable media such as magnetic tape,
a ROM, integrated circuit, or a magneto-optical disc.
Alternatively, the monitoring software is installed onto storage
device 34 of processing module 20 using an installation program,
and it is executed using microprocessor 36.
The present invention is not limited to using a microprocessor, a
reduced instruction set computer (RISC) processor or a hardware
state machine may be used to determine the presence of damage to a
structure.
In yet another aspect, the monitoring software may be implemented
by using an Application Specific Integrated Circuit (ASIC) (not
shown) that interfaces with processing module 20.
FIG. 4 illustrates the internal architecture of a NDM, such as NDMs
12, 14, 16, 18 of FIG. 1, according to one aspect of the present
invention. A distributed sensor interface 48 on the NDM is
connected to a set of sensor arrays, such as sensor arrays 4, 6, 8,
10 in FIG. 1, on a structure. Sensor arrays contain a fixed maximum
number of sensors, such as transducers, divided into fixed maximum
number of quadrants (described below with reference to FIG. 5). The
number of quadrants and transducers per quadrant are dependant on
the size of the sensor or transducer array and the number of NDM
transducer input channels.
In one aspect, there are nine transducers per quadrant and eight
quadrants per array; however the number could be greater or
smaller, depending on transducer layout and equipment constraints.
Each NDM simultaneously acquires data from all transducers within
each quadrant reducing the transducer acquisition time to less than
1 ms for each quadrant and less than 8 ms for an entire array in
the case of nine transducers/quad and eight quads/array. As shown
in FIG. 4, sensor interface 48 is connected to nine groups of
transmission lines 51-67 with eight transmission lines in each
group. Each transmission line in a group represents a different
quadrant in an array.
Groups of transmission lines 51-67 are connected to a protection
circuit 50 to protect against spikes in data and are then input
into a sensor quadrant to ADC input channel matrix map 69. As there
are only 45 unique inputs (as there are 45 sensors), matrix map 69
makes duplicate connections for sensors that are in one or more
quadrants. For example, referring to FIG. 5 below, sensor 11 is
located in quadrants Q0, Q1, Q4 and Q5. The duplicate connections
are then input into a single input of a plurality of multiplexers
52-68, one multiplexer for each sensor array on the structure. The
sensor data from each sensor array is multiplexed onto separate
single channels 70-86 hence, a large parallel input captures data
from nine channels/nine sensors simultaneously. Using single
channels 70-86 allows for a more efficient means of communications,
i.e., going to a higher speed bus with fewer wires and allowing
data to be taken close to real time. Each of the single channels
70-86 is then transmitted through an amplifier; low pass filter
(LFP) and an analog to digital (A/D) converter prior to being
transmitted to a computational engine 88. A configured PROM 90
programs computational engine 88 for all NDM behavior. Ethernet
port 94, transformers 96, 98 and connectors 100, 102 allow each NDM
to communicate with processing module 20. Power supply 92 is used
to power the NDMs.
Transducers are typically electro-mechanical conversion devices
that convert mechanical strain or motion to electrical currents
and/or voltages and vice-versa. Although in the preferred
embodiment, the sensors are transducers, any sensor that results in
a voltage or current source may be used and monitored.
Each NDM may operate simultaneously allowing all transducers
attached to processing module 20 to be monitored in less than 10 ms
during passive damage detection. All NDM activities are
synchronized using a common, low-speed clock allowing the stimuli
from one NDM to be acquired by surrounding NDMs during active
damage detection. Transducers may also be monitored for extended
periods of time, such as during monitoring for hard landing events
of the aircraft, using a memory bank swap technique that allows
transducer data to be stored for 30 seconds, and then swapped with
another memory for another 30 seconds, while the first memory is
uploaded to processing module 20. This process can be repeated
until the memory limitations in processing module 20 are reached
(greater than 30 minutes).
FIG. 5 illustrates an exemplary transducer array 104, according to
one aspect of the present invention. Transducer array 104 comprises
up to 45 sensors, 0-44 and is divided by the NDM into eight
sections or quadrants Q0-Q7, where each quadrant provides nine
transducers. FIG. 6 illustrates an example of a quadrant 106 in a
transducer array, according to one aspect of the present invention.
The NDM provides nine, parallel, input channels (groups of
transmission lines 51-67 in FIG. 4) that are multiplexed to each
quadrant.
Each NDM within system 5 stimulates a sensor in the sensor array
and captures the wave data as it propagates through the structure.
FIG. 7 illustrates an electrically stimulated sensor PZT0 causing
the structure to produce and propagate a surface wave (or path)
107a to a second sensor PZT1. The characteristics of the propagated
wave 107b when it arrives at sensor PZT1 contain information about
this particular path in the structure. The system of the present
invention uses all paths between all sensors to create a complete
structural picture under the transducer array.
FIG. 8 illustrates an example of usable path data from a single
stimulated sensor PZT21 in transducer array 104. When sensor PZT1
is stimulated 16 waves or paths are propagated. The NDM collects
data from all 16 paths. As shown in FIG. 8, the 16 paths are:
PZT21-PZT2; PZT21-PZT10; PZT21-PZT11; PZT21-PZT12; PZT21-PZT4;
PZT21-PZT13; PZT21-PZT14; PZT21-PZT20; PZT21-PZT22; PZT21-PZT28;
PZT21-PZT29; PZT21-PZT30; PZT21-PZF31; PZT21-PZT20; PZT21-PZT38;
and PZT21-PZT40. It should be noted that all the sensors in
transducer array 104 must be stimulated to get a complete picture
of the structural health.
FIG. 9 is a flow chart illustrating the steps for active
interrogation, i.e. detecting structural damage using an active
system, according to one aspect of the present invention. In step
S900, a structure is stimulated by stimulating a sensor in a sensor
array on the structure. A sensor is stimulated by applying a
waveform to the sensor or transducer generating waves on the
surface of the structure. In step S901, the sensor data is acquired
using an echo or another sensor located some distance away. In
other words, the structure is stimulated using a transducer and
then that or another transducer acquires the data. Steps S900 and
S901 are repeated until all sensors in all sensor arrays on the
structure have been stimulated and the sensor data has been
collected.
In step S902, the sensor data is collected by computational engine
88 and is uploaded to processing module 20 for analysis. The
sensors may not transmit the data that is in a format readable by
corrective system 22, which is where all the data goes.
Computational engine 88 collects a series of data samples from each
sensor that represents a waveform that has been captured over a
period of time. That waveform will then be processed by processing
module 20 to determine how fast the wave was traveling as well as
determining if there were any echoes in the wave. For example, if a
characteristic of a structural defect exists when a wave is
propagating across it, a reflection from the beginning part of the
defect and also from the back part will be seen. By propagating the
wave in multiple directions, a composite can be built that shows
the defect including the shape, using an intersection of all the
reflections. The sensor data is being fused together into one
picture of the structure.
In step S903, the acquired data is compared with the threshold
values stored in the processing module to determine if there is
damage to the structure. In step S904, based on the compared data,
the presence of any damage is detected. Finally, in step S905, a
corrective system is notified for corrective action. Notification
can be to the aircraft maintenance system, an alarm, an email or a
phone call to technician--service department.
FIG. 10 is a flow chart illustrating the steps for detecting
structure damage using a passive system, according to one aspect of
the present invention. In a passive system, the system uses the
same sensors as in the active system, but the structure is not
stimulated. Instead, the sensors simply listen to the structure
characteristics to detect any impact or stress event. For example,
in an aircraft sitting on a tarmac, the sensors are monitoring
around the cargo doors and if a truck or another vehicle came up
and hit the side of the aircraft, the aircraft could detect the
damage and either alerts the maintenance system or the crew or
ground crew. If an impact or stress event was detected, an active
interrogation, as described above with reference to FIG. 9, could
be immediately performed to see what the level damage was, if any.
The active and passive systems work together for maintaining the
integrity of the area around the areas that are being monitored,
such as doors.
Referring again to FIG. 10, in step S1000, sensors in the form of
sensor arrays are laid out on a structure. In step S1001, sensor
data is continuously acquired. In step S1002, the sensor data is
processed for analysis. In step S1003, the acquired data is
compared with the threshold values stored in processing module 20.
In step S1004, based on the compared data, a determination of an
impact or stress event is made. In step S1005 an active
interrogation (as described above with reference to FIG. 9) is
performed and compared with previously stored threshold levels to
detect damage. Finally, in step S1006, a corrective system is
notified for corrective action. Notification can be to the aircraft
maintenance system, an alarm, an email or a phone call to
technician--service department. The event is a high-energy impact,
which can be estimated, based on the response from the sensors.
FIG. 11 illustrates an example of acquiring structural path data
from a single sensor as illustrated in FIG. 8. The NDM accomplishes
each path acquisition by stimulating transducer PZT21 and using
nine input channels 0-8 to multiplex them amongst the eight
quadrants. The stimulation of PZT21 is described with reference to
FIG. 8. As can be seen in FIG. 8, six different quadrants have
transducers from which data needs to be collected, Quad 0, Quad 1,
Quad 2, Quad 4, Quad 5 and Quad 6; so six acquisition cycles are
required 106-116. In acquisition cycle 1 106, PZT21 is stimulated
and the nine input channels 0-8 on Quad 0 are acquired. In
acquisition cycle 2 108, PZT21 is stimulated and the nine input
channels 0-8 on Quad 1 are acquired. In acquisition cycle 3 110,
PZT21 is stimulated and the nine input channels 0-8 on Quad 2 are
acquired. In acquisition cycle 4 112 PZT21 is stimulated and the
nine input channels 0-8 on Quad 4 are acquired. In acquisition
cycle 5 114, PZT21 is stimulated and the nine input channels 0-8 on
Quad 5 are acquired. In acquisition cycle 6 116, PZT21 is
stimulated and the nine input channels 0-8 on Quad 6 are
acquired.
The NDM accomplished all of the path data acquisitions in the
example shown in FIG. 11 in six separate acquisition cycles, each
taking about 341 us. For six quadrants, that's 2 ms total. All
paths between 45 transducers can be stimulated and acquired in
about 123 ms.
The same steps as described in FIGS. 8 and 11 are applied to each
sensor in all the sensor arrays on the structure.
Since each NDM is independent in SHM system 5 of the present
invention, all transducer arrays in an SHM System can be stimulated
and acquired in the same time of 123 ms. So, the time required to
interrogate a structure is independent of the number of transducer
arrays in SHM System 5.
Prior art systems do the same path acquisition, but only work with
two transducers at a time. So to accomplish the path acquisitions
in FIG. 4, prior art systems would have to stimulate PZT 21, then
acquire data on PZT 20, then Stimulate on PZT 21, then acquire data
on PZT 10, and so forth until all 16 paths were acquired. Using the
same path time of 341 us, it would take about 6 ms, three times
longer. To capture all paths between 45 sensors (over 44
paths/stimulus.times.45 stimuli) would take 675 ms (5 times
longer).
FIG. 12 illustrates an example of interrogating a structure between
two or more adjacent transducer arrays 118, 120. Each NDM 122, 124
stimulus and acquisition activities may be synchronized such that
sensors on an adjacent or second transducer array 120 may acquire
stimulus originating from a first transducer array 118. A
processing module 126 (similar to processing module 20) will setup
the required activities of each NDM (stimulate or acquire) then
provide a synchronization signal to all NDMs to start their
respective activities. The process to acquire all the paths between
sensors on adjacent transducer arrays is exactly the same as
described above. Each sensor on the array boundary is stimulated,
then each adjacent array quadrant is acquired, exactly the same as
illustrated in FIG. 11.
Each NDM accomplishes the passive mode, i.e. listening to the
structure for impact or stress events, almost approaching
real-time, in exactly the same manner as the active mode only no
stimulus is used. The advantage of using the passive method is that
it is much faster than the active mode. A complete scan of a
transducer array can be accomplished in 2.7 ms, and given the
independence of the NDMs in the SHM System architecture of the
present invention, all sensors can be scanned in 2.7 ms. Most
impact or stress events of damage magnitude occur over tens to
hundreds of milliseconds, so several scans will be made of the
structure during these events eliminating the possibility of
missing a damaging stress or impact event.
FIG. 13 illustrates an example of pulse--echo acquisition, when the
NDM acquires signals produced by a stimulated sensor after the
stimulus has ended. This is known as Pulse-Echo acquisition. This
mode provides information about edges near the stimulated sensor
and also the condition of the sensor itself. Instead of acquiring
the wave data at another sensor, the wave data is an echo or
reflected wave from an edge of the structure.
The NDM acquires data whose signal dynamic range is greater than 65
dB under these circumstances. To do this, the NDM employs
switchable gain stages, reducing the gain (Av=0.1) during the
stimulus generation time, then increasing the gain (Av=25) during
the "listening" time, acquiring data during the entire activity.
The health of each stimulated sensor can be determined by analyzing
the pulse-echo data, thus allowing automatic detection of failed
sensors. The NDM automatic acquires Pulse-Echo data every time a
stimulus is generated.
The method and system of the present invention is advantageous over
prior art systems in that the present invention provides for the
simultaneous capture of sensor data from sensor arrays reducing
acquisition time. Hence, fast damage detection is achieved while
minimizing the cost, weight and size of the system. Furthermore,
the present invention can monitor and inspect large areas of a
structure, such as a wing of an aircraft.
While the present invention is described above with respect to what
is currently considered its preferred embodiments, it is to be
understood that the invention is not limited to that described
above. To the contrary, the invention is intended to cover various
modifications and equivalent arrangements within the spirit and
scope of the appended claims.
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